1. Field of the Invention
The present invention relates to improvements in the high-resolution optical addressing of picture elements (pixels) and more specifically to a device for effecting such optical address and image scanning and/or printing apparatus employing such device.
2. Description of the Prior Art
Recently, it has been found that light valve array devices provide a highly useful vehicle in electronic imaging. One preferred light valve configuration comprises a piece of ferro-electric ceramic material, such as lanthanum-doped lead zirconate titanate (PLZT), which is sandwiched between crossed polarizers and electrically activatible to operate in a Kerr cell mode. An array of such light valves comprises such crossed polarizes and a panel of PLZT material that has a plurality of electrodes formed on one of its major surfaces. The electrodes are arranged in a manner facilitating the selective application of discrete electrical fields across (in a direction perpendicular to the direction of viewing) discrete surface areas which constitute pixel portions of the panel. Upon application of such fields, the PLZT material becomes birefringent and rotates the direction of polarization of incident light by an extent dependent on the field magnitude. This results in transmission of light through the PLZT pixels and cooperating polarizers varying as a function of the respective addressing fields.
My U.S. Pat. No. 4,229,095 discloses various embodiments of electronic color-imaging apparatus that utilize such light valve arrays to effect multicolor exposure of panchromatic recording media. For example, a color image is formed electronically by selectively opening and closing individual light valves of such arrays in synchronization with the energization of red, green and blue exposing sources and according to the red, green and blue color information for the pixels of that image. One preferred embodiment disclosed in that patent comprises a linear light valve array disposed in spaced transverse relation to the recording media feed path. The pixels of the array are addressed concurrently with image information, a line at a time, and the movement of the recording medium, and the red, green and blue color exposures are synchronized with successive actuations of the linear array.
It can be appreciated that light valves must address many image pixels per line in order to form images having even moderate detail. The number of pixels per line increases in accordance with the resolution requirements of the imaging application, e.g. becoming as large as 250 pixels per inch or larger for high quality continuous tone imaging. Each pixel of the recording medium must be independently addressable with light in accordance with the unique content of the image to be reproduced. Therefore, discretely activatible electrode means has been provided for each pixel portion of the light valve array, and each electrode means has had its own high voltage "off-on" switch, e.g. a transistor amplifier. The cost and complexity of these many switches and their connection and packaging present problems in electronic imaging with light valve devices.
One solution to minimize such problems is to provide a smaller number of transversely-spaced pixel portions in the light valve array and then effect multiple passes of the recording medium, with a transverse-indexing of the array (or recording medium) between passes. Thus, if light valve pixel portions are spaced with a three-pixel inter-space and the recording medium is transported past the light valve array four times, only one-fourth the usual number of high-voltage switches is required. However, multiple passes require additional time and can present registration problems.
Another solution, described in my U.S. application Ser. No. 268,975, entitled "Light Valve Devices and Electronic Imaging/Scan Apparatus with Locationally-Interlaced, Optical Addressing", filed June 1, 1981, employs cooperating high and low resolution light valve arrays to effect electronic imaging in an electronically efficient mode. This latter approach is highly advantageous for many applications; however, it is not highly light-efficient. In certain applications this can be a shortcoming.